The present invention relates to a fuel cell including a housing, at least one proton-conducting first ply, which is covered on both sides by catalyst plies, gas-permeable electrodes on the catalyst plies, and second plies in the form of electrically conductive plates arranged on the catalyst plies and on both sides of the first plies, which second plies are in electrically conductive contact with the electrodes in close proximity and delimit, together with the electrodes, gas-conducting channels, the first ply being in contact with the second ply with an essentially even surface.
Such a fuel cell is known from the journal Spektrum der Wissenschaft, July 1995, page 98. In this cell, the channels are molded into bipolar plates running parallel to one another. Therefore they are expensive and complicated to manufacture. The high weight/performance ratio of the known fuel cell is not fully satisfactory.
In fuel cells the ionic and electric paths are separated during the reaction between hydrogen and oxygen in order to obtain electrical energy from chemical energy.
The design and operation of different types of fuel cells are described by K.-D. Kreuer and J. Maier in Spektrum der Wissenschaft, July 1995, pp. 92-96.
The electrodes used in fuel cells must be very good electron conductors (electrical resistance around 0.1 xcexa9xc2x7cmxe2x88x921) . In addition, they must not inhibit the chemical reaction. Furthermore they must be compatible with the electrolytes and the catalyst and must be chemically and physically inert, i.e., they must not enter into undesirable reactions with one another under the strongly oxidizing conditions at the cathode or the strongly reducing conditions at the anode.
In order to connect a plurality of cells to form cell stacks, the electrodes arranged between the first and second plies must have sufficient mechanical strength. Furthermore, material and process costs, service life, and environmental compatibility have an important role.
The object of the present invention is to provide a fuel cell of the type described above such that it can be industrially manufactured in a simpler and less expensive manner.
This object is achieved according to the present invention with a fuel cell of the type discussed above by providing that the electrode be formed of at least one layer of electrically conductive fibers made of polymeric material.
In the fuel cell according to the present invention, the electrodes are formed by at least one layer of carbonized fibers made of a polymeric material, traversed in at least one direction by flow channels running parallel to their surfaces.
The carbonized fibers are in contact with the catalyst plies, as well as the conductive plates in close proximity, which ensures proper removal of the electrons released during the intended application, as well as proper mechanical support for the first and second plies through one another. The thickness of the first and second plies can therefore be reduced resulting in considerable improvement in the weight/performance ratio compared to known fuel cells. A secondary result is the reduction of the volume required fore unit power generated. Therefore more fuel cells can be installed in a given space than previously, which is advantageous in automotive applications and improves overall available power output.
The fuel cell according to the present invention has design advantages in that it does not require that gas-conducting channels be formed using mechanical machining and subsequently sealing in a complicated manner; in the fuel cell according to the present invention all plies may have an even design in the simplest case, which considerably simplifies manufacturing and sealing and provides the additional advantage that the first ply is available almost in its entirety for proton conduction and the second ply is entirely available for electron removal.
It has been proven advantageous if the layer forming the electrodes is made of nonwoven, woven, or knitted fabric. The fibers should have a titer of 10 to 15 dtex, preferably 15 to 35 dtex. The layer preferably has an overall weight per surface area of 15 to 250 g/m2 to for a thickness of 1to 6 mm.
The layer may have a multi-ply structure similar to that of corrugated paper and may have at least one central support ply having an open structure between two cover plies of a higher density for optimally performing different functions. One of these functions may be to provide optimum support of the proton-conducting first ply, for which contact points in close proximity from one another seem to be advantageous. The second function is to provide optimum removal of the electrons generated during the intended application via the conductive plates, and the third function may be optimum exposure of the first ply to the operating gases needed during the intended application, while avoiding an unnecessary pressure drop, which requires, among other things, the electrodes facilitate the flow parallel to their surfaces; in particular, a design in which the fibers forming the support ply are arranged essentially perpendicular to the cover plies performs these functions particularly well. The fibers may also be arranged in the path of the gases enclosed in channels and be formed, for example, by warp stitch joints or by separately produced filaments which are introduced in the gap between the cover plies and optionally bonded thereto. The fibers forming the electrodes are preferably made of an electrically conducting polymeric material such as, for example, carbonized polyacrylnitrile or pitch. Metals can also be used. The fibers may have a smaller diameter in the area of the cover plies then in the area of the support ply in order to achieve optimum electron conductivity with the least possible resistance to flow.